Qqman

- Minor fix to location to referenced image for pandoc self-contained README.html generation.

- Annotate SNPs below a p-value threshold with the `annotatePval=` option. See vignette for details.
- Annotate the top SNP on each chromosome with the `annotateTop=` option. See vignette for details.

- Does not assume that SNPs are evenly distributed across chromosomes when deciding where to place the tick in the center of the chromosome.
- Changed single chromosome x-axis notation to use Mb instead of raw pos
- `qq()` accepts graphical parameters the same way as `manhattan()`
- Removed default `xlim`
- Citation details on package load
- Added axis label options
- Removed `ymax` argument in favor of allowing user to set `ylim` in `...`
- Option to _not_ take log of p-value

Version 0.1.1 on CRAN. Minor changes to vignette.

Same as previous release, archiving for ZENODO